Photosynthesis

11. Carbon and energy requirements of autotrophic organisms are fulfilled

Carbon and energy requirements of autotrophic organisms are fulfilled by:

[amp_mcq option1=”Photosynthesis” option2=”Gluconeogenesis” option3=”Glycogenesis” option4=”External sources” correct=”option1″]

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UPSC NDA-2 – 2015
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Autotrophic organisms, such as plants and some bacteria, synthesize their own organic compounds for energy and carbon requirements. The primary process by which most autotrophs achieve this is photosynthesis, using light energy to convert carbon dioxide and water into glucose (a carbohydrate) and oxygen.
Autotrophs obtain their carbon and energy through processes like photosynthesis or chemosynthesis.
Gluconeogenesis and Glycogenesis are metabolic pathways primarily occurring in heterotrophic organisms (like animals) or for storage/synthesis within the organism, not the means by which autotrophs *initially* acquire carbon and energy from external inorganic sources. External sources are what heterotrophs consume.

12. Leaves of most plants appear green because the chlorophyll present in

Leaves of most plants appear green because the chlorophyll present in it :

[amp_mcq option1=”absorbs red and blue light while reflecting green light.” option2=”absorbs green light only.” option3=”absorbs green light while reflecting red and blue light.” option4=”reflects red light and absorbs blue and green light.” correct=”option1″]

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UPSC NDA-1 – 2024
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Leaves of most plants appear green because the chlorophyll present in it absorbs red and blue light while reflecting green light.
Chlorophyll is the primary pigment in plants responsible for photosynthesis. It absorbs light most strongly in the blue and red regions of the visible spectrum. The green light from the spectrum is not absorbed efficiently; instead, it is reflected by the leaves. This reflected green light is what our eyes perceive, making the leaves appear green.
The absorption spectrum of chlorophyll shows peaks in the blue (~430 nm) and red (~662 nm) wavelengths and a trough in the green (~550 nm) wavelength, corresponding to reflection. The energy from the absorbed red and blue light is used for photosynthesis.

13. The gaseous product of a process in plants is a requirement for anothe

The gaseous product of a process in plants is a requirement for another vital process that releases energy. Given below are four combinations of the process and product. Identify the correct answer.

[amp_mcq option1=”Respiration and Nitric oxide” option2=”Transpiration and Water vapour” option3=”Photosynthesis and Oxygen” option4=”Germination and Carbon dioxide” correct=”option3″]

This question was previously asked in
UPSC NDA-1 – 2021
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The correct answer is C) Photosynthesis and Oxygen. Oxygen is a gaseous product of photosynthesis and is a requirement for aerobic respiration, a vital process that releases energy in most organisms, including plants.
– Photosynthesis is the process by which plants convert light energy into chemical energy (glucose) using carbon dioxide and water, releasing oxygen as a byproduct.
– Respiration is the process by which organisms break down organic molecules (like glucose) to release energy. Aerobic respiration requires oxygen and produces carbon dioxide and water.
– The question describes a gaseous product (oxygen from photosynthesis) being a requirement (for respiration) of a process that releases energy.
– Transpiration produces water vapour, which is not a requirement for energy release.
– Nitric oxide is not a standard product of respiration or a requirement for energy release in typical metabolic pathways.
– Germination is a process, not a gaseous product. While respiration provides energy for germination, carbon dioxide is a product of respiration, not a requirement for it.

14. In plants, which one of the following gases is released during Photosy

In plants, which one of the following gases is released during Photosynthesis ?

[amp_mcq option1=”Carbon dioxide” option2=”Oxygen” option3=”Hydrogen” option4=”Methane” correct=”option2″]

This question was previously asked in
UPSC NDA-1 – 2015
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Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment. The overall equation for photosynthesis is: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$. The gases involved as reactants are Carbon dioxide ($\text{CO}_2$), and the gas released as a product is Oxygen ($\text{O}_2$).
Knowing the inputs and outputs of the photosynthesis process.
Plants take in carbon dioxide from the atmosphere and water from the soil. Using light energy, they convert these into glucose (a sugar) and release oxygen into the atmosphere. This process is vital for maintaining the Earth’s atmosphere composition and providing the basis for most food chains.

15. Which one of the following would be a suitable plant to test that chlo

Which one of the following would be a suitable plant to test that chlorophyll is necessary for photosynthesis?

[amp_mcq option1=”Lady Plymouth” option2=”Cactus” option3=”Cuscuta” option4=”Oleander” correct=”option1″]

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UPSC Geoscientist – 2023
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To test if chlorophyll is necessary for photosynthesis, you need a plant that has some parts with chlorophyll and some parts without chlorophyll. Variegated leaves, which have green (chlorophyll present) and non-green (chlorophyll absent) patches, are ideal for this experiment. After exposing the plant to light and testing for starch (a product of photosynthesis) using iodine solution, the green parts will test positive (turn blue-black), while the non-green parts will test negative (remain brownish), demonstrating that chlorophyll is required for starch production during photosynthesis. Lady Plymouth (Pelargonium zonale) is a common plant species with variegated leaves often used for this demonstration.
– Experiment requires comparison between parts of a plant with and without chlorophyll.
– Variegated leaves are suitable for this purpose.
– Green parts contain chlorophyll, non-green parts do not.
– Testing for starch after photosynthesis reveals which parts photosynthesized.
Cactus leaves are modified into spines (though the stem is photosynthetic); Cuscuta is a parasitic plant that lacks chlorophyll and obtains nutrients from a host; Oleander has uniformly green leaves. None of these are typically used for a simple experiment demonstrating the necessity of chlorophyll using variegation.

16. Which one of the following colours of the visible spectrum of light is

Which one of the following colours of the visible spectrum of light is least absorbed by the green plants?

[amp_mcq option1=”Violet” option2=”Red” option3=”Green” option4=”Yellow” correct=”option3″]

This question was previously asked in
UPSC Geoscientist – 2022
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Green plants appear green because they reflect or transmit green light rather than absorbing it significantly for photosynthesis.
– Photosynthesis primarily utilizes light from the blue and red ends of the visible spectrum, as chlorophyll pigments absorb these wavelengths most effectively.
– Green light is poorly absorbed by chlorophyll, hence it is reflected or transmitted, making the plants appear green.
The absorption spectrum of chlorophyll a and chlorophyll b shows peaks in the blue-violet and red regions, with a dip in the green region. While some green light is absorbed by accessory pigments like carotenoids, the overall absorption is lowest for green light compared to other colours essential for photosynthesis.

17. Photosynthesis that converts light energy into chemical energy by the

Photosynthesis that converts light energy into chemical energy by the plants, involves the use of green pigments of leaves called chlorophyll. The only structure in a leaf that hosts chlorophyll is :

[amp_mcq option1=”Nucleus” option2=”Ribosome” option3=”Chloroplast” option4=”Chromosome” correct=”option3″]

This question was previously asked in
UPSC CDS-2 – 2024
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Photosynthesis, the process by which plants convert light energy into chemical energy, primarily takes place in specialized organelles called chloroplasts. Chloroplasts contain the green pigment chlorophyll, which absorbs light energy necessary for the photosynthetic reactions. While other cell structures are involved in the overall life of the leaf cell, chlorophyll is specifically located within the chloroplasts.
– Chloroplasts are the site of photosynthesis in plant cells.
– Chlorophyll, the main light-absorbing pigment, is located on the thylakoid membranes within chloroplasts.
The nucleus contains the cell’s genetic material. Ribosomes are involved in protein synthesis. Chromosomes are structures within the nucleus that carry genetic information. None of these structures host chlorophyll or are the primary site of photosynthesis.

18. Which one of the following statements about the process of photosynthe

Which one of the following statements about the process of photosynthesis is correct ?

[amp_mcq option1=”Light energy is directly converted to kinetic energy which oxidizes carbon dioxide.” option2=”Light energy is directly converted to chemical energy which causes reduction of water.” option3=”Chlorophyll absorbs the chemical energy of light which causes oxidation of carbon dioxide.” option4=”Chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.” correct=”option4″]

This question was previously asked in
UPSC CDS-2 – 2022
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Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment. This process involves converting light energy into chemical energy.
– Chlorophyll absorbs light energy from sunlight.
– This light energy is used to split water molecules (photolysis of water) into oxygen, protons, and electrons. This is the oxidation of water.
– The energy captured and the electrons/protons generated are then used to reduce carbon dioxide into glucose (a sugar). This is the reduction of carbon dioxide.
Thus, chlorophyll absorbs light energy which causes splitting of water molecules and reduction of carbon dioxide.
The overall equation for photosynthesis is 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂. The process occurs in two main stages: the light-dependent reactions (where light energy is captured and water is split) and the light-independent reactions (Calvin cycle, where CO₂ is reduced to sugar).

19. Chlorophyll in photosynthetic prokaryotic bacteria is associated with

Chlorophyll in photosynthetic prokaryotic bacteria is associated with

[amp_mcq option1=”plastids” option2=”membranous vesicles” option3=”nucleoids” option4=”chromosomes” correct=”option2″]

This question was previously asked in
UPSC CDS-2 – 2019
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Photosynthetic prokaryotic bacteria, such as cyanobacteria, lack membrane-bound organelles like chloroplasts (which contain chlorophyll in eukaryotes). Instead, their photosynthetic pigments, including chlorophyll, are embedded within internal membrane systems. These membrane systems can take various forms, including flattened sacs, tubules, or vesicles, which are often referred to as chromatophores or thylakoids depending on their arrangement, and are essentially membranous structures or vesicles.
Chlorophyll in photosynthetic prokaryotes is not contained within plastids but is located in specialized internal membrane structures within the cytoplasm.
Plastids (like chloroplasts) are organelles found in eukaryotic cells (plants and algae). Nucleoids are the regions where the prokaryotic genetic material is located. Chromosomes refer to the structured form of DNA.

20. A leaf was plucked from a plant on a sunny day and kept for 2 minutes

A leaf was plucked from a plant on a sunny day and kept for 2 minutes in boiling water. It was subsequently immersed in boiling alcohol and treated with iodine solution. What will be the final colour of the leaf after the test?

[amp_mcq option1=”Colourless” option2=”Green” option3=”Blue” option4=”White” correct=”option3″]

This question was previously asked in
UPSC CDS-1 – 2023
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After treating the leaf with iodine solution following de-colourisation, the final colour will be blue (specifically blue-black).
This experiment is a standard test for the presence of starch in a leaf, which is a product of photosynthesis. Keeping the leaf on a sunny day ensures starch production. Boiling water kills the cells. Boiling alcohol removes the chlorophyll, making the leaf pale so the colour change with iodine is visible. Iodine solution turns blue-black in the presence of starch.
The steps are designed to isolate the starch and make its detection by iodine possible. Removing chlorophyll is crucial because it would mask the colour change. A leaf from a plant kept in darkness for a day or two would show no starch and would remain brown/yellow with iodine.
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